1. Field of the Invention
This invention relates generally to the field of elastomeric rolls and the like used for feeding paper sheets, photographic paper or other documents and a method of manufacture thereof. More particularly, this invention relates to a new and improved sheet feeding roller or other member comprised of a foamed epichlorohydrin elastomer without processing aids and migratory additives, wherein the roller or other member is characterized by a high initial coefficient of friction and low hardness.
2. Brief Description of the Related Art
An enormous number of paper sheets and other documents such as currency, personal checks and films are handled by a variety of document handling devices, including office copiers, automatic teller machines, typewriters, printers, calculators, computers and many other types of business equipment. As used herein, the word "document" means any thin sheet of material, such as paper, including photographic paper, the other documents mentioned previously, and other similar sheets of material. Often associated with the document feeding of these devices are elastomeric rolls, wheels, pads, belts and the like, which act to convey the documents along a desired path. Documents are delivered into the document handling devices by the elastomeric feed components, such as a roll, through frictional force which develops from imparting motion to the feed roll while it is in contact with the document. The document is moved forward when the feed roll is rotated, if the frictional force is sufficiently high to prevent slippage. The frictional force increases with increased elastomer coefficient of friction (COF) and with increased normal force exerted on the elastomer/document interface.
Although the remaining description herein uses elastomeric feed rolls to illustrate the pertinent concepts, feed rolls are used to simplify the description of the field of document feeding, and not to imply any limitation of this geometry. It should be understood that the same concepts apply to wheels, belts, pads, and other geometries of components used for document feeding.
The use of an elastomeric material in the construction of a feed roll is well known in the art, and various elastomers have been used in the fabrication of feed rollers. For example, in U.S. Pat. No. 4,173,058 to Stieger there is disclosed a method for manufacturing photographic film processing rollers. An adhesive primer is applied to a cylindrical metal rod and a melted polymer comprising an elastomeric urethane resin on its surface is deposited on the metal rod by means of a cross-head extrusion die. The extruded coating is then hardened. U.S. Pat. No. 4,287,649 to Kohler also discloses a paper feeding roller made of a core of foamed cellular resilient material and an annular skin of a relatively hard elastic material disposed on the core.
Elastomeric feed rolls are made of hard, solid elastomers such as SBR (styrene butadiene rubber), neoprene, natural rubber, synthetic polyisoprene or several others. These solid elastomers possess high coefficient of friction and high compressive modulus. However, preferred document feed rolls comprise a low compression modulus (high compliance) cellular elastomer. These rolls result in large contact area (footprint) and low contact pressure. Document skewing and damage, and elastomer wear are eliminated or greatly reduced. Such feed rolls are commonly cellular polyurethane elastomers, one of which is described in U.S. Pat. No. 4,287,649 to Kohler.
One drawback to the use of the above mentioned materials is that these materials require the use of processing aids, plasticizers, and/or other additives when producing a solid elastomer feed roll. A processing aid is generally incorporated into the elastomer compound in order to promote flow of the compound under shear or heat. Commonly used processing aids include fatty acid soaps such as stearic acid, paraffinic materials, and low molecular weight polyethylene or other olefinic materials, among many others. A plasticizer is incorporated in the material to increase its workability, flexibility, or distensibility. Commonly used plasticizers include DOA (bis(2-ethylhexyl) adipate) and DOP (bis(2-ethylhexyl) phthalate), among many others. Other commonly used migratory additives include various surfactants and compatibilizers used to stabilize the foam and to compatibilize the elastomer blends. The above-described additives are migratory, and their use in solid elastomer feed rolls and other paper feeding components has been shown to impair the surface of photographic paper by marking the paper's surface when it is used in a paper feed device.